The production of substituted phosphines can be complicated if all of the substituents on the phosphorus atom are not identical. In situations where the production of mixed substituted phosphines is desired, the method of production generally involves the use of an organo alkali metal intermediate, the synthesis of which is often difficult or inefficient.
One class of bidentate phosphorus ligands which are mixed alkyl-aryl diphosphines has become of interest as precursors of catalyst compositions useful in the production of a class of polymeric materials known as polyketones or polyketone polymers. These polyketones are linear alternating polymers of carbon monoxide and at least one ethylenically unsaturated hydrocarbon. Such polymers have repeating units of the formula ##STR1## wherein D is a moiety of ethylenically unsaturated hydrocarbon polymerized through the ethylenic unsaturation. Processes for the production of such polymers are illustrated by published European Patent Application Nos. 0,121,965 and 0,181,014 and copending U.S. Pat. No. 4,806,630. The processes usually involve a catalyst composition formed from a compound of a Group VIII metal selected from palladium, nickel or cobalt, the anion of a strong non-hydrohalogenic acid and a bidentate ligand having two Group VA atoms which are preferably phosphorus. Particularly useful as the bidentate phosphorus ligand is the mixed alkyl-aryl diphosphine of the formula ##STR2## wherein R.sup.1 independently is an aryl substituent, and R is a divalent alkylene or substituted alkylene bridging group, often the trimethylene group.
Good results are obtained in the production of polyketones when the phosphine precursor of the catalyst composition is of the above formula wherein each R.sup.1 is phenyl and R is trimethylene, the ligand therefore being 1,3-bis(diphenylphosphino)propane. One of the least complicated methods of producing this type of ligand is through the reaction of an alkali metal di(R.sup.1) phosphide, e.g., sodium diphenylphosphide, and an .alpha.,.OMEGA.-dihaloalkane such as 1,3-dichloropropane. Corresponding methods produce other bis(diarylphosphino)alkanes.
Recent process developments in polyketone production have shown that particularly good results are obtained on occasion when at least one of the aryl groups has a polar substituent, particularly an alkoxy substituent, in at least one of the ring positions ortho to the phosphorus. Such bidentate phosphorus ligands are represented by the above formula wherein at least one R.sup.1 has an alkoxy substituent in a ring position ortho to the phosphorus, e.g., at least one R.sup.1 is 2-alkoxyphenyl or 2,6-dialkoxyphenyl.
Monophosphine ligands of the general formula P(A).sub.3 wherein each A is individually an organic substituent tend to make less reactive catalyst compositions than the diphosphine ligands. However, copending U.S. patent application Ser. No. 088,169, now U.S. Pat. No. 4,859,764, establishes that monophosphines having one or more similar or different heterocyclic substituents that contain one or more oxygen, sulphur, or nitrogen atoms in a five or six-membered ring, which ring is bound to the phosphorus atom by one of the carbon atoms in the ring, affords catalyst compositions with attractive activities for the polymerization of carbon monoxide with one or more olefinically unsaturated compounds. Examples of suitable heterocyclic-substituted monophosphines, which may be regarded as being derived from triphenyl phosphine by substitution of one or two of the phenyl groups with a nitrogen-containing heteroaromatic substituent, are: 2-(diphenylphosphino)pyridine, 2-(diphenylphosphino)-1-methylpyrrole, 2-(diphenylphosphino)-1,3,5-triazine and bis(2-pyridyl)phenylphosphine.